Control system for refrigerating apparatus



Feb. 24, 1942.

CONTROL E. S. LAMMERS, JR

SYSTEM FOR REFRIGERATING APPARATUS Filed April 18, 1956 2 Sheets-Sheet 1 21 o IL O k O m INVENTOR Euww aumnzzs ATTOR Y Feb. 24, 1 ,942. E. s. .LAMM E RS JR- 2,274,336

CONTROL SYSTEM FOR REFRIGERATING APPARATUS Filed April 18, 193 6 2 Sheets-Sheet 2 llji i INVENTOR EDWINS.LHMMERS ATTOR Patent ed Feb. 24,-

- UNITED STATES PATENT OFFICE I cou'rnor. sis-rm roa aemrosns'rmo msna'rus Edwin S. Lammers, Jr., Atlanta, Ga., assignor to Westinghouse Electric {a Manufacturing Company, East Pittsburgh, Pa., a corporation of 4 Pennsylvania Application April 18, 1936, Serial No. 75,078

. 3 Claims. My invention relates to control systems for refrigerating apparatus, more particularly to a control system for refrigerating apparatus employing a plurality of refrigerant compressors. and it has for an object to provide an improved system of this kind.

A further object of my invention is to provide an improved method and apparatus for controlling refrigerating apparatus having a plurality of refrigerant compressor elements'o'fequal or various capacities, wherein the compressor elements are selectively operated, individually or ,together, in accordance with the prevailing-load and in such manner that the total capacity of the elementsin operationis optimum for the mrevaili'ng load. v

A further object of my invention is to regulate the operation of the refrigerant compressor eleorators; and,

Fig. 2 is a diagram of the trical connections for controlling of the system shown in Fig. 1.

In Fig. 1, I have shown my improved refrigerating system applied to a plurality of enclosures vmentsin accordance with the total capacity of the evaporators that are operating.

Myinvention is particularly adaptable to air conditioning systems having a pluralityof evaporators for cooling the air in a plurality of spaces and supplied with refrigerant by a plurality of parallel connected, refrigerant compressor elements which may be ofvarious sizes. It is desirable in a system of this kind to operate the smallest size condensing unit that will carry the existing load,-and, also, to operate the least number of units.

In accordance with my invention, I provide a control system for a plurality of parallel connected, refrigerant compressor elements, which may be of various sizes, wherein an electrical control circuit is employed. 'A characteristic of the circuit such as, for example, the current therein is varied in response to the load on the system or the total capacity of the evaporators which are operating. A current responsive device is connected in the circuit and operates to control the operation of the compressor elements in accordance with the current in the circuit and, therefore, the load on the system or the capacity of the evaporatorsinoperation.

v The current responsive device such as, for ample, 9. Kelvin balance, isactuated by the current in the circuit and assumes various positions in response to the diflerent values of current in the circuit. The various positions of the balance determine the size and number of the compressor elements to be operated for the existing load.

By operating the compressor elements, either individually or together, so that the total capac- 18 to ill, inclusive, for cooling the air therein. A plurality of refrigerantievaporators It to 2|, inelusive, are provided for cooling the air in the enclosures It to l5, respectively. each of said evaporators it to 2| being provided with a suitable refrigerant expansion device 22 such as, for example, a conventional thermostatic expansion valve. Such a valve, which is well known in the art, controls the flow of refrigerant to the evaporator to maintain a constant degree of superheat of the refrigerant vapor exhausted from the evaporator, thereby supplying the evaporator substantially with -such quantity as can be evaporated therein. A plurality of motors, 25 to 30,

inclusive, are associated with the respective evaporators It to 2i and operate to drive fansor blowers 3| for the translation of air in heat exchanging relation with the evaporators prior to its delivery to the enclosures. 1

Operation of the various evaporators may be controlled by a plurality of valves 22 to 31, inclusive, which are connected between the expansion devices 22 and a common refrigerant supply ity thereof is of-the lowest value suiiicient for c rryi the existing oad. more emcient oner 5 in the compressed refrigerant, either a common conduit 40. The valves 32 to 31, are operated e1ectrically,"preferablyby means of solenoids II to V4', inclusive. Vaporized refrigerant is conveyed from the evaporators It to 2| by means of a common suction conduit 41-. v

A plurality of refrigerant compressor elements generally indicated at'ilh'il, and" are emplayed for compressing therefrigerant vapor withdrawn'from the, suction conduit 41. The compressor elements 50, BI, and 52 include a plurality of compressors, '55. and $8 driven, re-

spectively, by motors 51, ",{and 59. Suitable condensing 'mechanisniis provided for condenscondenser or separate condensers being employed. Preferably, as shown in the illustrated embodiment, each compressor is provided with a condenser 6i. Refrigerant condensed by the condensers Bi is delivered to a reservoir or liquid receiver 53 by means of a common conduit 62, said reservoir 53 being in communication with the liquid conduit Ml. The heat load of the various enclosures ill to IE may be of various values, so that diiIerent sizes or capacities of.

evaporators are necessary. 'In the system disclosed, it will be assumed that the capacities of the evaporators it to M, inclusive, are, respectively, 6, 8, 10, 12, and is tons. As described hereinafter, the evaporators may be selectively operated either individually or together, so that it will be obvious that the load on the compressor elements til, 6i, and 52 may vary from 4 tons to a total load oi 54 tons. The compressor elements are also operated singly or simultaneously in different combinations depending upon the load imposed thereon. It will be assumed in the present example that the capacities of the compressors 5%, 5b, and d6 "are, respectively, 1 tons, tons, and 20 tons.

In accordance with my invention, I provide means, as disclosed hereinafter, for automatically efiecting operation of the smallest compressor element that will carry the prevailing load and, furthermore, which will efiect operation of the least number oi condensing units at all times. Reference will now be had to Fig. 2, wherein the eontrolsystem for the apparatus shown inl ig. l is diagrammatically shown.

The source of power for the control devices is represented by the conductors L-i and lie-2. The compressor motors til, til, and are energized from power mains ltd-l and M which may also represent the source of power for the fan motors to did, inclusive.

The fan motors 25 to 33d, inclusive, are controlled by switches 55 to it, inclusive, which may be manually opened and closed, preferably, from their respective enclosures iii to iii. A plurality of switches ii to 76, inclusive, are opened and closed simultaneously with the opening and closing of switches til to it and control circuits having a plurality of solenoids Ti to 82, inclusive, connected therein. The latter circuits are also controlled by respective thermostats 88 to Sit, inclusive, arranged in the respective enclosures it to id, as described hereinafter, control the operation of the evaporator-s in response to the temperature of the air in their associated enclosures. It will be apparent from the foregoing that energization of a fan motor is efiected in order to render its associated evaporator operative, so that delivery of air to the evaporator is assured before refrigerant can be delivered to the evaporator. Operation of the fan motors 25 to 3d may be efiected, without cooling of the air delivered thereby, in any suitablemanner mou n in the art; for example, by providing a plurality of hand-operated switches st! to {it in circuit with the thermostats 83 to $8. Any of the'circults including the thermostats E3 to 88 may be rendered ineffective to permit the delivery of refrigerant to the evaporators by opening its associated hand switch 89 to 9d.

Thevalve solenoids ll to C6 are shown in Fig. 2

' controlled by switches to 400, inclusive; said switches being closed by their respective solenoids IT to 82 when the latter are energized. The solenoids 11 to 82, when ener d, also close respective switches IOI to I, inclusive, which are respectively connected in series with resistors it? to H2. The resistors it! to H2 are connected in parallel in a circuit indicated by the reference numeral H3 and regulate the value of a characteristic thereof such as, for example, the value of the current flowing therein.

Control of the compressor motors 5t, 5t, and '59 is effected by a mechanism including a Kelvin balance, indicated generally at I Iii and including series connected, stationary and movable coils Hit and i ii, respectively, which are connected in the circuit iiii. Energization of the circuit M3 may be efiected by the secondary of a transformer N8, the primary lid of which is energized from the conductors L-i and L-2.

The moving coils ii? of the balance iiti are carried by a beam it! pivoted at B22 and carrying a contact are connected to the conductor L-i.

The latter contact is engageable with stationary contacts i2 1 and i and defines therewith a double-throw switch. A spring lid is connected at one of its ends to the beam i2i and at its other end to a pivoted lever H21, the latter being rotated about the pivot point E22 by a travelling nut i283 carried by a screw 529. Rotation of the screw are is efiected by a reversible motor, the

armature of which is shown at liii. Preferably,

a speed reducing device is employed between the armature wt and the screw its, which device is indicated at 982. The field of the reversible motor is split, the portions 033 and BBQ of which are connected at one side to the stationary contacts tit and its, respectively. Both field portions its and 635 are connected, at their opposite sides to the armature i3i,-the latter being connected to the conductor L-Z as shown.

From the foregoing, it will be apparent that the value of the current flowing in the circuit i i3 and in the coils of the balance its will va y dependent upon the number and resistance values of the resistors iii to i 62 that are connected in circuit. The resistors it? to its are connected in the circuit Mil simultaneouslywith the energization of their respective valve solenoids ii to ift, so that, as refrigerant is admitted to an evaporator by its associated solenoid valve, a resistor is connected in the circuit H3 and the current therein is increased The values of the resistances of the various resistors W! to 602 are predetermined and are inversely proportional to the tonnage capacity of their respective evaporators, so that the values of the current flowing through the respective resistors are proportional to such tonnage capacity. The value of the current in the circuit M53 and the balance Mb is the sum of the current flowing through the several resistors and it is, therefore, proportional to the total capacity of the evaporators that are operating.

As the operation of a Kelvin balance is well understood, it will not be described here, other than to say that the current in the coils 6- iii bias the beam iii in clockwise direction with a force proportional to the value of the current. A spring we biases the beam iii in counterclockwise direction in opposition to the force-of the cells. The spring is of such strength and scale that as the nut i123 reaches the proper position corresponding to the value of the current in the circuit M3, the spring exerts a bias on the beam i2! equal to the bias of the coils Iii-l IT, causing the beam Hi to assume equilibrium position in which the contact I23 does creases, due to an evaporator being rendered active, the beam I2I rotates in clockwise direction and causes engagement of 'the'contacts I23 and I28. The armature I3l is, thereby, energized and effects rotation of the screw I28 in such manner that the nut I28 moves toth'e right. The pivoted lever I21 therefore rotates aboutthe pivot point- I22 in counterclockwise direction, adding bias to the spring I25 and returning the beam I2I to its neutral position. The contacts I23 and I25 are disengaged and the armature I3I stops.

A decrease in the current in the balance coils I I6-I I 1, due to the termination of flowof refrigerant to an evaporator and disconnection of its respective resistor from the circuit II3, effects a reverse operation of the balance mechanism II5, the beam I2I' tilting in counterclockwise direction to engage contacts I23 and I2l. Accordingly, the armature I3I effects a movement of the utilized for regulating the operation of the compressor motors in, as, and is, which operation is thereby responsive to the total tonnage of the evaporator-s which are active. A plurality of mechanically operated switches I35 to I38, inclusive, may be disposed adjacent to the nut I28 and actuated thereby. A projection IlI carried by the nut I28 engages the switches I35 to I38 and effects closing and openingthereof as the nut I 28 moves to the right and left, respectively. It will be understoodthat the switches I35 to I38 remain in the position to which they have been moved by the projection Ill. The switches I35 to I38 that are engaged and closed by the pro-! jection I as it moves to the right, remain closed until engaged by the projection I as it moves to the left at which time they are opened.

A plurality of solenoids 2 to I48, inclusive, are connected between the conductors LI and L2 and are controlled by the switches I'35 to I38, inclusive. In the drawing, the solenoids 2 I82 and I83, which switch is moved, periodically, from one position to the other, whereby the starting and stopping sequence of the motors 58 and 58 is reversed.

. Operation As shown in the the switches'll to 18 are open. Assume it is desired to condition the control system for ventilating all of the enclosures I8 to I5, inclusive,

and for maintaining the air therein at the temperature at which the thermostats are set. The

' ,oi the thermostat contacts. 'As cooling of the switches 85 to 18, inclusive, are closed for initiating operation of the fans 25 and 38, inclusive. Switches 'II- to 15, inclusive, are closed incidental to the closing of the switches 55 to 18,50 thatthe circuits including the solenoids 11 to 82, ,inciusive, are conditioned for operation, that is, placed in condition to be'energized upon closing air in all of the enclosures is to be eilfected, manually operated switches 88 to 84, inclusive, are closed. The operation of each evaporator will now be controlied' by its associated thermostat.

Assume now that cooling is required in the enclosures I8 and II which include the 4 and 6 ton evaporators I5 and I1, respectively. The thermostats 83 and N are, therefore, closed while the remaining thermostats 85 to 88, inclusive. are" in their open position. The solenoids 11 and 18 are, therefore, energized and switches 85, 88,

III, and I82 are closed. Accordingly, the valve 1 solenoids H and l2 are open for the passage of refrigerant to the evaporators I5 and I1. Closing of the switches IM and I82 connects the resistors I81 and I88 in circuit with the balance H5. The amount of current passed by the resistors I81 and I88 is proportional to 10. tons evaporator capacity, and the balance 5 responds to, this current value in such manner that the nut I28 is moved to the right a sufllcient distance to effect closing of switch I35. A circuit is established from the line conductor L--I through the switch I35, interlock switch I58,

' o solenoid m, to the conductor 1.4.

The switch I" is thereby closed and the swltcli I52 opened. Closure of the switch I" eflects energization of the solenoid I5I which operates to close the switch I51. Closure of the switch I81 to H5, inclusive, are shown deenergized'. When energized, they eflect closing of respective switches 1 to I5I. The solenoids-Il2 to M5,

inclusive, open respectiveinterlock switches I52 to I55, inclusive, when energized. The interlock. switches I 52, I53, I58, and I55 are, respectively,

connectedin series with the switch I, the solenoid M2,. the switch I58, and the solenoid Ill.

The various conductors interconnecting thevarious switches I" to I55, inclusive, are clearly shown on the drawing and it is not-deemed necessary to recite their specific connections.

The compressor motors 51, 58, and 58 are controlled by relay switches I51, I58, and-I58 operated, respectively, by solenoids I5I, I82, and I53. Energization of the latter solenoids is, under the control of the switches I" to I52, inclusivaand switch I54. As described hereinafter, themotors 51, 58, and 58 are started and stopped in a predetermined sequence and, as the motors 58 and 58, as disclosed, are of ,the same capacity, their relative sequence of operation may. be periodically reversed in order to equalize the wear thereon and on their driven compressors. Accordingly, a conventional double pole reversing switch I85 initiates operation ofthe motor 51 and the 14-. 8

ton compressor 5l driven thereby.

As recited heretofore, the capacity of the evaporators I8 and I1 is 4 and 6-tons respectively ora total of 10 tons. This load can readily be car ried by the small or 14-ton compressor. I Assume now that the thermostat 85 closes for effecting cooling in the enclosure I2, the thermostats 83 and 84- remaining closed. This operation energizes the .solenoid 18 which closes the switches 81 and I83. The solenoid 43 is enersized by theclosing of the switch 81 for permitting the flow of refrigerant to the evaporator I8. Closing'of the switch I83 connects the resistor I88 in circuit so that there is an increased flow of currentin the balance II5, the value of current now being proportionate to 18 tons evaporator capacity. As described. heretofore, the con- .tacts I28 and I25 engageand the armature I3I rotates to cause further movement of the nut I28 to the right. This movement causes the projection I to close the switch I33.- A circuit is therefore established which eflects energization "of the solenoid 3, thereby closing the switch may be interposed in' the circuits of the solenoids drawings, the control system is in its shutdown position, due to the fact that I45 and opening the interlocked switch I53. Opening of the latter deenergizes the solenoid I42 and switches I41 and I52 open and close respectively. Opening of the switch I61 deenergizes the solenoid II and terminates operation of the motor 51 and the l i-ton compressor driven thereby. Closing of the switches I52 and M8 establishes a circuit from the conductor L-I through switches I52, I48, reversing switch 565, which is in its lower position, solenoid I62 to the line conductor L--2. solenoid I52 closes the switch I58 and thereby initiates operation of the motor 58 and the 20- ton compressor 55 driven thereby.

It will be seen from the foregoing that the load on the compressor elements is now 18 tons which is greater than the capacity of the compressor 5-3 but within the capacity 01' the compressor 55.

Assume now that the enclosure It requires cooling and that the thermostat 85 closes. This will represent a load of 28 tons. thermostat 85 efiects energization of the valve solenoid it so that refrigerant is delivered to the evaporator I9. The resistor II5 is also inserted in the circuit N3 of the balance II5 which operates to effect the closing of switch IN. A circuit is therefore established from the line conductor L--I, switch I37, interlock switch I55, solenoid I45 to the other line conductor L'2.

, Energization of the solenoid I44 eflects closing of the switch I59 and opening of the switch I545. The solenoid IGI is therefore energized by a circuit extending from the conductor L-I, switch I49, solenoid I6I, to the line conductor L-2. The switch I5! is therefore closed for initiating operation of the motor 51 and the l4-ton compressor driven thereby. The total load of 28 tons is now carried by the 14 and 20-ton compressors 51 and 55.

Assumenow that the enclosure I I4 requires cooling and that the thermostat ll closes. The solenoid valve 45 is energized to admit refrigerant to the evaporator 20 and the resistor III inserted in the circuit of the balance H5. The latter operates to close the switch I35 whereby the solenoid I45 is energized. The circuit is established from the conductor LI through the switch I35, solenoidI45 to the line conductor L-2. The solenoid I45 operates to open the switch I 55 and to close the main switch I50. The opening of th switch I55 deenergizes the solenoid I44 thereby opening switch I49 and Energization of the closed. As the latter switch I39 closes, the solenoid I45 is energized for closing the switch IN. The latter establishes a circuit through the solenoid IGI .so that the switch I5? is closed for initiating operation of the motor 5? and the i i-ton compressor 55. All elements are now operating.

Closing of the The foregoing is a description of the operation of the various elements of the control system as the compressors are started. A description of the operation of system as the load is decreased will now be given.

Assume the temperature of the air in enclosures I3 and It is depressed to the desired value. The thermostats E5 and 58 open and deenergize the solenoids t5 and 52 so that switches 98, Hit, I05, and I55 open. Accordin ly, th valve solenoids 45 and .15 are deenergized and the valves and 57! close to terminate flow of refrigerant to the evaporators I9 and 2 I. As described heretofore, the fan motors 25 and til continue to operate for circulating untreated air in the enclosures I5 and 05. Opening of the switches SE36 nism M5 efiects counterclockwise movement oi closing the switch I54. As the switch I49 opens, 1

the solenoid I5I is deenergized so that switch I51 opens and operation of the motor 51 and the 14-ton compressor is terminated. Closing of the switch I50 establishes a circuit from the conductor L-I through switch I50, switch I54, reversing switch I 55, solenoid I63 to the line conductor L-Z. The switch I58 is therefore closed as the solenoid I63 is energized and operation of the motor 59 and the 20-ton compressor 56 is initiated. It will be seen that the load on the compressor elements is' now an even 40 tons which is within the capacity of the two 20-ton compressors which are operating.

With all of the enclosures demanding cooling, it will be apparent that all of the solenoid valves will be open and that the current flowing in the balance I I5 is maximum due to the fact that all the resistors are in circuit. The travelling nut I28 is therefore at its extreme right position so that all of the switches I35 to I 39, inclusive, are

the beam Ill and engagement of the contacts I 23 and I245. The motor armature Iii and held portion I 33 are energized and rotation of the screw I29 is eiiected for moving the nut I28 and projection MI to the left to a location corresponding to 30 tons of refrigeration load. This location is intermediate the switches I3? and I38. As the projection I4I passes from its extreme right position to the recited location, it moves, successively, the switches I39 and I38 to their open positions. 1

Accordingly, the solenoids I45 and I56 are deenergized, whereby the switches I55 and I5I open and the interlock switch I55 closes. Solenoid I44 is energized by switch I55 so that switch I49 closes and switch- I55 opens. As switch I55 opens,-

It is to be understood that any of the many known expedients commonly used in the electrical control art may be employed wherever occasion for their use arises. For example, suitable time delay devices, such as dashpots, may be applied to the relay switches I5'|-'I59 to provide sequential starting of the motors 51-58 upon restoration of the electrical current after an interruption thereof. i

From the foregoing, it will be apparent that I have provided an-improved refrigerating system having a plurality of compressors which may be of various sizes connected with a plurality of evaporators, wherein the compressor to be operated is selected in accordance with the prevailing load and wherein a minimum number of compressors are operated at all times. It is to be understood that the present invention is also applicable where compressors of equal capacity are used. For example, the compressor 54 and the motor 51 may be omitted, in which case the relays in, I44 and 146 would also be omitted.

Furthermore, it will be apparent that I provide an improved refrigerating -system having a control or phantom circuit in which the value of an electrical characteristic is proportionately varied in accordance with the load on the system, and

the compressor or compressors to be Operated selected in accordance with the value of the electrical characteristic.

While. I have shown my invention in but one form', it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications, without departing from the spirit thereof, and I desire, therefore; that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

j 1. -In refrigerating apparatus, the combination of a plurality of evaporators, a control device associated with each evaporator forinitiating and terminating operation thereof, variable capacity compressor means for serving said evaporators, and means for varying the compressor capacity in operation substantially in proportion to the total capacity of the evaporators that are controlled to' operate, .said last-mentioned means comprising a group of resistors respectively associated with the several evaporators and having resistance values-inversely proportional to the capacities of the associated evaporators, each resistor being energized by the control device of the associated evaporator-simultaneously with eflect,

' ing operation of the latter, said resistors being connected in parallel when energized, and means responsiveto the total current flowing through ,the' resistors that are ener zed for varying the .total'compress'or capacity substantially in pro- -.i:portion to. such current and. therefore, substam.

tially in proportion to'the total capacity of the evaporators that are controlled to operate;

2. In refrigerating apparatus, the combination of evaporator means of variable capacity, control means for varying the evaporator capacity in operation, variable capacity compressor means .for serving said evaporator means, and means for varying the compressor capacity in operation in cuit.

, tal current flowing through the resistors 3. In a control system, the combination of a plurality of load-imposing elements, a control device associated with each element for initiating and terminating operation thereof, motor-actuated means for carrying the load imposed by said elements, and means for controlling said motoractuated means comprising a group of resistors respectively associated with the load-imposing elements and having resistancevalues inversely proportional to the loads imposed by the associated elements, each resistor beingenergized by the control device of the associated element simultaneously with effecting operation of the lat ter, said resistors being connected in parallel when energized, and means responsive to the to that are energized for controlling the operation of the motor-actuated means to-assume a-load substantially equal to the total load of the-elements that are controlled to operate.

s. Lemmas, .m. 

